Ch. IV, 5] ARRANGEMENTS OF LEAVES 



141 



h 



i 



VI 



forming two vertical ranks and bringing the third leaf over 



the first (Fig. 95), as well manifest in Corn and other 



Grasses. In other cases, the leaves stand 



one-third of the circumference apart, 



forming an obvious spiral, bringing the 



leaves into three vertical ranks with a 



fourth over a first (Fig. 96), as in Sedges, 



which, correlatively, have triangular 



stems. The next of the arrangements 



actually found is that where the leaves 



stand two-fifths of the circumference 



apart (Fig. 97), in which case the spiral 



must turn twice around the stem before 



a leaf, the sixth, is reached over the first, 

 five vertical ranks 

 resulting. This is 

 the commonest of 

 the alternate ar- 

 rangements. It is 

 very clear in the 

 Apple, and in many ment 

 common p ] ants, 



though at times, in long stems, its regu- 

 larity is disturbed by some twist of the 

 stem. It underlies the prevalence of the 

 number five in the plan of most flowers, as 

 the one-third and one-half arrangements 

 underlie the numbers three and four in 

 others. The next arrangement is that 

 of three-eighths (Fig. 98), found in the 

 Holly. The next is that of five-thir- 



^°j7pi-i T a h -!,g:: teenths ( F 'g- ")- found in the House - 



leek, which forms the familiar rosettes, 

 while in Pine cones and other such struc- 

 tures, arrangements of eight twenty-firsts, and even thirteen 

 thirty-fourths and twenty-one fifty-fifths have been deter- 



Fig. 96. — The alter- 

 nate, g spiral, arrange- 



nate 

 ment 



